Conventionally, a wind turbine generator feedback-controls a speed of the generator. For example, when a voltage of a utility grid drops and an output power of the generator reduces instantly, a load is eliminated, and thus the speed of the generator rises. However, a pitch angle of wind turbine blades is controlled to a feather side so that the rise in the speed is repressed and the rotation of the generator is stopped.
For example, Patent Document 1 describes a technique that controls the pitch angle of the wind turbine blades through an output power supplied from an uninterrupted power supply when a low voltage event such as a drop in a voltage of a utility grid occurs.